Subdivide and re-weight parallel/sibling bones? (or, how to deform-rig lips)
You can simply select the armature, in edit mode use shift D to duplicate some lips bones, place them where you want them (the duplicated will have the same parent-child relationships), then in pose mode select all lips bones, go to object mode, shift select the mesh, go to weight paint mode and use the weights menu &quot;Automatic assign from (selected) bones&quot;.
Make some manual weight adjustments if  needed.